Structure of Pearls

Abstract

IN a recent paper by Dr. Orton and myself (Jour. Marine Biol. Assoc., vol. 14, No. 4, in the press) it has been pointed out that a thin, brown horny layer occurs in the form of a skin on the inner surface of the shell of oysters (Ostrea edulis), and is especially well developed in those from the Fal Estuary beds, in addition to the four normal strata found in the shells of lamellibranchs. This layer was found to peel off in specimens collected in the autumn of 1926, thus indicating that it was secreted at the end of the autumn period of growth. Layers of similar material have been found by us in sections of oyster shells (O. edulis) and by Römer in the shell of Margaritana (Zeitschrift für wissensch. Zoologie, 1903, 437, Taf. XXXI., Fig. 14), alternating with layers of nacreous material. It is well known from the work of Herdman and Jameson that the structure of pearls from Margaritifera vulgaris is intimately related to the structure of the shell, and that new shell growth and pearl growth are probably comparable phenomena. It is also known that layers of brown material similar to that found in shells are also found in some pearls. The occurrence of a layer of brown horny material on or in the shells of O. edulis indicated, therefore, that similar layers might be found in the pearls taken from O. edulis.